Light olefins (defined herein as ethylene, propylene, butenes and mixtures thereof) serve as feeds for the production of numerous important chemicals and polymers. Light olefins traditionally are produced by cracking petroleum feeds. Because of the limited supply and escalating cost of petroleum feeds, the cost of producing olefins from petroleum sources has increased steadily. Efforts to develop and improve olefin production technologies, particularly light olefins production technologies, based on alternative feedstocks have increased.
An important type of alternative feedstocks for the production of light olefins are oxygenates, such as alcohols, particularly methanol and ethanol, dimethyl ether, methyl ethyl ether, methyl formate, and dimethyl carbonate. Alcohols may be produced by fermentation, or from synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials including coal, recycled plastics, municipal wastes, agricultural products, or most organic materials. Because of the wide variety of raw material sources, alcohol, alcohol derivatives, and other oxygenates have promise as an economical, non-petroleum feedstock source for olefin production.
The conversion of oxygenates to olefins takes place at a relatively high temperature, generally higher than about 250.degree. C., preferably higher than about 300.degree. C. Because the conversion reaction is exothermic, the effluent typically has a higher temperature than the initial temperature in the reactor. Many methods and/or process schemes have been proposed to manage the heat of reaction generated from the oxygenate conversion reaction inside of the reactor in order to avoid temperature surges and hot spots, and thereby to reduce the rate of catalyst deactivation and reduce the production of undesirable products, such as methane, ethane, carbon monoxide and carbonaceous deposits or coke. It would be very useful to have a process that effectively utilizes the heat of reaction contained in the products exiting the oxygenate conversion reactor, optimizes heat recovery, and reduces overall utility consumption in the conversion of oxygenates to olefins. Such a process is environmentally, economically, and commercially more attractive.